Gettering regions and methods of forming gettering regions within a semiconductor wafer

ABSTRACT

In one aspect, the invention pertains to a method of forming a gettering region within an Si semiconductor wafer, the method including: a) providing a semiconductor material wafer; b) providing a background region within the semiconductor material wafer, the background region being doped with a first-type conductivity enhancing dopant, the first-type conductivity enhancing dopant being either n-type or p-type; c) implanting a second-type conductivity enhancing dopant into the background region to form a second-type implant region entirely contained within the background region, the second-type conductivity enhancing dopant being of an opposite type than the first-type conductivity enhancing dopant of the background region; and d) implanting a neutral-conductivity-type conductivity enhancing dopant into the second-type implant region to form a metals gettering damage region entirely contained within the second-type implant region. The invention also pertains to gettering region structures.

TECHNICAL FIELD

This invention relates generally to methods of forming gettering regionswithin silicon semiconductor wafers and to gettering regions formed bysuch methods.

BACKGROUND OF THE INVENTION

Impurity contamination of Si semiconductor wafers is a problem withinthe semiconductor industry. Of particular concern are metalliccontaminants, such as iron, nickel and copper. When such impurities arepresent in a Si semiconductor device, the impurities degrade thecharacteristics and reliability of the device. As integration insemiconductor devices becomes increasingly dense, the tolerance formetallic contaminants becomes increasingly stringent.

Among the methods for decreasing metallic contamination in semiconductorwafers are methods for improving cleanliness in plants which manufacturesuch semiconductive devices. However, regardless of how many steps aretaken to insure clean production of semiconductor devices, some degreeof contamination by metals is inevitable. Accordingly, it is desirableto develop methods and structure for isolating metallic contaminantspresent in semiconductor wafers from devices which are ultimately formedwithin and upon such wafers. The act of isolating these contaminants isgenerally referred to as gettering, as the contaminants are gathered, orgettered, to specific areas within a semiconductor wafer.

Conventional processes for gettering metallic contaminants often focuson creating defects or damage within a semiconductor wafer in a regionwhere gettering is sought to occur. Generally, such gettering regionsare formed well below the regions of a wafer where device formation willultimately occur and separated from such regions by an expanse ofsubstrate. Two embodiments of such prior art methods are shown withreference to FIGS. 1 and 2. Referring to these figures, a semiconductorwafer 10 comprises a front-side surface 12 and a back-side surface 14.Front-side surface 12 is defined as a surface where device formationwill ultimately occur. A damage region 16 is formed beneath front-sidesurface 12 and is placed deep enough within the substrate that laterdevices formed on front-side surface 12 are isolated from the damageregion 16. Damage region 16 is typically formed by introducingimpurities into the lattice of the semiconductor material of wafer 10.In FIG. 1, damage region 16 is a layer within the middle of substrate10, while in FIG. 2, damage region 16 is a layer along back-side 14 ofwafer 10. After damage region 16 is formed, wafer 10 is heated to drivemetallic contaminants into the damage region.

A problem of increasing concern as semiconductor devices becomeincreasingly smaller is substrate-background current, or diffusioncurrent. Such diffusion current is function of device temperature andincreases exponentially with temperature. Thus, if the temperature of asemiconductor wafer increases, such as typically occurs during operationof semiconductor devices, the diffusion current generally alsoincreases. At a given temperature, more diffusion current will generallyform from a defect region of a semiconductor wafer than from a regionwithout defects. Thus, damage regions 16 tend to generate more diffusioncurrent at a given temperature than do other regions of a semiconductorwafer 10.

The diffusion current electrons formed in damage region 16 willgenerally drift away from damage region 16, potentially towardfront-side surface 12. Such electrons at front-side surface 12 maydegrade the performance of devices that are later formed on surface 12.

For the above-described reasons, it would be desirable to develop agettering region which could collect diffusion current electrons. Also,since hole counterparts of the diffusion current electrons can also begenerated as the diffusion current electrons are generated, it wouldalso be desirable to develop a gettering region which could collect suchholes.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a diagrammatic fragmentary sectional view of a semiconductorwafer fragment containing a gettering region of a type known in theprior art.

FIG. 2 is a diagrammatic fragmentary sectional view of a semiconductorwafer fragment containing a gettering region of a type known in theprior art.

FIG. 3 is a diagrammatic fragmentary sectional view of a semiconductorwafer fragment shown at a processing step in accordance with theinvention.

FIG. 4 is a view of the FIG. 3 fragment shown at a processing stepsubsequent to that shown in FIG. 3.

FIG. 5 is a view of the FIG. 3 wafer shown at a step subsequent to thatof FIG. 4.

FIG. 6 is a view of the FIG. 3 wafer shown at a step subsequent to thatof FIG. 5.

FIG. 7 is an expanded view of area 7 of FIG. 6 showing one embodiment ofthe invention.

FIG. 8 is an expanded view of area 7 of FIG. 6 showing an embodiment ofthe invention different from the embodiment shown in FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws "to promote the progressof science and useful arts" (Article 1, Section 8).

In one aspect of the invention, the invention is a method of forming agettering region within an Si semiconductor wafer comprising thefollowing steps:

providing a semiconductor material wafer;

providing a background region within the semiconductor material wafer,the background region being doped with a first-type conductivityenhancing dopant, the first-type conductivity enhancing dopant beingeither n-type or p-type;

implanting a second-type conductivity enhancing dopant into thebackground region to form a second-type implant region entirelycontained within the background region, the second-type conductivityenhancing dopant being of an opposite type than the first-typeconductivity enhancing dopant of the background region; and

implanting a neutral-conductivity-type conductivity enhancing dopantinto the second-type implant region to form a metals gettering damageregion entirely contained within the second-type implant region.

In another aspect of the invention, the invention is a method of forminga gettering region within an Si semiconductor wafer comprising thefollowing steps:

providing a semiconductor material wafer;

implanting phosphorus within the semiconductor material wafer to form aphosphorus implant region therein;

implanting silicon within the semiconductor material wafer to form asilicon implant region; and

the step of implanting silicon occurring simultaneously with the step ofimplanting phosphorus.

In yet another aspect of the invention, the invention is a getteringdiode within an Si semiconductor material wafer comprising:

a background region within the semiconductor material wafer, thebackground region comprising a first-type conductivity enhancing dopant,the first-type conductivity enhancing dopant being either n-type orp-type;

a second-type conductivity implant region entirely contained within thebackground region, the second-type implant region comprising asecond-type conductivity enhancing dopant, the second-type conductivityenhancing dopant being of an opposite type than the first-typeconductivity enhancing dopant; and

a metals gettering damage region entirely contained within thesecond-type implant region in the semiconductor material, the first-typebackground region and the second-type implant region together forming agettering diode which surrounds the damage region.

More specifically, the invention relates to methods of forming getteringregions within silicon semiconductor wafers and of forming getteringdiodes which may collect positive or negative charges, as eitherelectrons or holes, depending on the polarity of the collector. Theinvention is further described with reference to FIGS. 3-5.

Referring to FIG. 3, a wafer 10 of semiconductor material, preferablysilicon, is provided. Wafer 10 preferably comprises a background region18 which is conductively doped with a first-type conductivity enhancingdopant (not shown). The first-type conductivity enhancing dopant iseither n-type or p-type, so that background region 18 is either ann-type or p-type region. Wafer 10 further comprises contaminants 20,which may include metallic contaminants, such as metallic contaminantsselected from the group consisting of iron, nickel and copper.

Referring to FIG. 4, a second-type conductivity enhancing dopant 22 isimplanted into background region 18 to form second-type implant region24 entirely contained within background region 18. Second-type dopant 22is of an opposite type than the first-type dopant. Thus, if backgroundregion 18 is n-type, implant region 24 is p-type, and vice versa.

In the embodiment of the invention in which background region is p-typeand dopant 22 is n-type, dopant 22 preferably comprises phosphorus. Insuch a preferred embodiment, phosphorus implant region 24 contains apeak concentration depth 26, which is defined as the depth at which themaximum concentration of phosphorus from phosphorus implant 22 is found.Typically, an implant such as implant 22 will produce a Gaussiandistribution of implanted material across a thickness "X". Thus, thepeak concentration depth 26 is typically found at approximately thecenter of implanted region 24. Preferably, dopant 22 is implanted at anenergy of 2800 KeV and a dose of from about 1×10¹² atoms/cm² to about5×10¹³ atoms/cm², with a most preferred dose being about 5×10¹²atoms/cm². Under such preferable conditions, the phosphorus peakconcentration depth 26 is greater than or equal to about 1 micronbeneath an outer surface 28 of the semiconductor material of wafer 10,and most preferably is greater than or equal to about 2 microns beneathan outer surface 28, and less than or equal to about 4 microns beneaththe outer surface. Also, under such preferable conditions, phosphorusimplant region 24 will have a thickness "X" within which substantiallyall of the implanted phosphorus is contained which is greater than about2 microns and less than about 5 microns.

In the embodiment of the invention in which the background region 18 isn-type and dopant 22 is p-type, dopant 22 preferably comprises boron. Inthis embodiment, implant 22 most preferably comprises atomic boron, andis preferably implanted a dose of from about 1×10¹² atoms/cm² to about5×10¹³ atoms/cm², and an energy of about 930 KeV.

Referring to FIG. 5, a neutral-conductivity-type dopant 30 is implantedto form a neutral-conductivity-type-dopant implant region 32 withinwafer 10. Neutral-type dopant 30 preferably comprises an elementselected from the group consisting of Si, O, C, N, Ar and Ge. Region 32is shown as being entirely contained within region 24, however, in otherembodiments of the invention which are not shown, region 32 may extendbeyond region 24. Regardless of whether region 32 is entirely containedwithin region 24, the implant of dopant 30 preferably forms a metalsgettering damage region 36 entirely contained within second-type implantregion 24.

Neutral-conductivity-type-dopant-implant region 32 has a peakconcentration depth 34 wherein the concentration ofneutral-conductivity-type-dopant is maximized. As shown, peakconcentration depth 34 preferably lies within implant region 24.

Damage region 36 has a thickness "Y", which is preferably from about 0.5microns to about 0.8 microns. Accordingly, if dopant 30 comprises atomicsilicon, the implant of dopant 30 is preferably conducted at an energyof from about 2500 KeV to about 2800 KeV and with a dose of from about9×10¹² atoms/cm² to about 9.5×10¹⁴ atoms/cm². Most preferably, the doseis about 1×10¹⁴ atoms/cm².

In the shown embodiment, neutral-conductivity-type-dopant 30 isimplanted after the implant of second-type dopant 22. However,neutral-conductivity-type dopant 30 could also be implanted before, orsimultaneously with, dopant 22. If dopant 30 is implanted simultaneouslywith dopant 22, dopant 30 is preferably comprises atomic silicon anddopant 22 preferably comprises atomic phosphorus. Under such preferableconditions, the atomic silicon will preferably be generated from asource gas comprising one or more of the compounds silicon hexafluorideand silicon hexachloride, and the atomic phosphorus will preferably begenerated from a source gas comprising phosphine.

Under the preferred conditions in which dopant 22 comprises phosphorusand dopant 30 comprises silicon, the total combined dose of the dopants22 and 30 is preferably from 1×10¹³ atoms/cm² to about 1×10¹⁵ atoms/cm²,and most preferably is about 1×10¹⁴ atoms/cm². Even though theneutral-type dopant 30 will generally make the largest contribution tothe formation of damage layer 36, the implant of second-type dopant 22will likely also create some damage to wafer 10. Thus, the totalcombined dose of dopant 22 and dopant 30 can be an important parameterto control in regulating the overall size of damage region 36.

Referring to FIG. 6, the wafer of FIG. 4 is shown subsequent to athermal processing step. As shown, the thermal processing step hasdriven metallic contaminants 20 into damage region 36. Thus,contaminants 20 are effectively gathered within the damage region 36, sothat the region functions as a gettering region 36. It will be notedthat neutral-type-dopant implant region 32 of FIG. 5 is not shown inFIG. 6. This is because a gettering thermal processing step willtypically diffuse neutral type dopant 30 throughout a semiconductormaterial. Accordingly, there will generally be no clearly definedneutral-type-dopant implant region 32 subsequent to such a thermalprocessing step.

FIGS. 7 and 8 illustrate expanded views of FIG. 6 and further illustratetwo separate embodiments of the invention. FIG. 7 illustrates anembodiment of the invention in which background region 18 is a p-typeregion and in which implant region 24 is an n-type region. In contrast,FIG. 8 illustrates the opposite arrangement of regions whereinbackground region 18 is an n-type region and implant region 24 is ap-type region. FIGS. 7 and 8 illustrate separate embodiments in which ap-type region and an n-type region together form a gettering diode 40which can be used to restrict the flow of electrons 42 within asemiconductor material 10 and to thereby contain the spurious electrons42.

Referring first to FIG. 7, the figure illustrates an embodiment of theinvention in which a damage region 36 is contained within an n-typeregion 24 which itself is contained within a p-type region 18. Together,n-type region 24 and p-type region 18 form the gettering diode 40. Asillustrated, a reverse bias is applied to the gettering diode 40 toeffectively contain diffusion current electrons 42 within n-type region24. In the shown embodiment, contaminants 20 are illustrated as metalliccontaminants "M" which have gettered into damage region 36.

Referring to FIG. 8, an embodiment of the invention is shown in which adamage region 36 is contained within a p-type region 24 which in turn iscontained within an n-type region 18. Together, n-type region 18 andp-type region 24 form a gettering diode 40 within which spuriouselectrons 42 are contained. As illustrated, a reverse bias is applied togettering diode 40 to contain holes 43 within p-type region 24. Suchholes 43 may, for instance, comprise the positive counterpart ofdiffusion current electrons 42.

Methods for applying reverse bias to diodes are generally known topersons of ordinary skill in the art.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

We claim:
 1. A method of forming a gettering region within an Sisemiconductor wafer comprising the following steps:providing asemiconductor material wafer; providing a background region within thesemiconductor material wafer, the background region being doped with afirst-type conductivity enhancing dopant, the first-type conductivityenhancing dopant being either n-type or p-type; implanting a second-typeconductivity enhancing dopant into the background region to form asecond-type implant region entirely contained within the backgroundregion, the second-type conductivity enhancing dopant being of anopposite type than the first-type conductivity enhancing dopant of thebackground region, the first-type background region and the second-typeimplant region together forming a gettering diode; implanting aneutral-conductivity-type conductivity enhancing dopant into thesecond-type implant region to form a metals gettering damage regionentirely contained within the second-type implant region, and applying avoltage bias to the gettering diode to effectively collect electronswithin the gettering diode.
 2. The method of claim 1 wherein theneutral-conductivity-type conductivity enhancing dopant comprises anelement selected from the group consisting of Si, O, C, N, Ar, and Ge.3. The method of claim 1 wherein the step of implanting theneutral-conductivity-type conductivity enhancing dopant occurs after thestep of implanting the second-type conductivity enhancing dopant.
 4. Themethod of claim 1 wherein the step of implanting theneutral-conductivity-type conductivity enhancing dopant occurs beforethe step of implanting the second-type conductivity enhancing dopant. 5.The method of claim 1 wherein the step of implanting theneutral-conductivity-type conductivity enhancing dopant occurssimultaneously with the step of implanting the second-type conductivityenhancing dopant.
 6. The method of claim 1 wherein the first-typeconductivity enhancing dopant is n-type and wherein the second-typeconductivity enhancing dopant is p-type.
 7. The method of claim 1wherein the first-type conductivity enhancing dopant is n-type, whereinthe second-type conductivity enhancing dopant is p-type, and wherein thesecond-type conductivity enhancing dopant comprises boron.
 8. The methodof claim 1 wherein the first-type conductivity enhancing dopant isn-type, wherein the second-type conductivity enhancing dopant is p-type,wherein the n-type background region and the p-type implant regiontogether form the gettering diode, and wherein the step of applying abias to the gettering diode comprises applying a reverse bias to thegettering diode.
 9. The method of claim 1 wherein the first-typeconductivity enhancing dopant is p-type and wherein the second-typeconductivity enhancing dopant is n-type.
 10. The method of claim 1wherein the first-type conductivity enhancing dopant is p-type, whereinthe second-type conductivity enhancing dopant is n-type, and wherein thesecond-type conductivity enhancing dopant comprises phosphorus.
 11. Themethod of claim 1 wherein the first-type conductivity enhancing dopantis p-type, wherein the second-type conductivity enhancing dopant isn-type, wherein the p-type background region and the n-type implantregion together form the gettering diode, and wherein the step ofapplying bias to the gettering diode comprises applying a reverse biasto the gettering diode.